He was coming off the field during last week’s preseason loss in Buffalo, a game in which the Vikings’ first-team offense was erratic and unproductive, scoring only three points on five drives.

“I was saying, ‘Oh, my gosh, what are we doing?’ ” Jennings said. “Like, we are struggling. And then I saw this guy on the sideline that had this 28 jersey on and he wasn’t dressed and I’m like, ‘Oh yeah, I forgot. We don’t have a big part of our offense out here, who draws a lot of attention.’ ”

That would be running back Adrian Peterson, who will make his preseason debut Sunday in San Francisco. Jennings’ point was that concern over struggles by the offense should be tempered by the fact that the team’s best offensive weapon has yet to play.

Still, there is a lot of improvement to be made, Jennings said.

“It jumped out as we watched the film,” Jennings said. “Just being fundamentally sound. They definitely played faster than us. They got to the point of attack quicker than we did — I mean as a whole. Individually, there were definitely things I feel like I could have done better as far as precision in my route running, different things to help the quarterback. But, as a unit, we just got outplayed.”

The Vikings starters will play into the third quarter Sunday in the third of four preseason games, against a top-quality opponent.

Jennings, who signed with the Vikings as a free agent in March after seven years with the Packers, welcomes the extra playing time.

“This is a new system, a new quarterback, a new team chemistry,” he said. “So I need the work. I’ve got to feel comfortable in the offense in a game setting.”

Kalil returns

Still, Vikings coach Leslie Frazier is looking for better offensive execution this week. And that starts with offensive line play. Left tackle Matt Kalil returned to practice after coming out of the Buffalo game because of a sore knee. Frazier said Kalil would play Sunday, and that the entire offensive front needs to be better.

“Especially when we’re going to be on the road, like we are in the opening game of the season, from a communication standpoint,” Frazier said. “That was one area where I felt we could have done a lot better, communicating some of the things we saw, and making sure we execute some of the things we have to get done, whether it be snapping the football back to the quarterback or identifying who the [middle] linebacker is in certain fronts. It should be better this week.”

Time enough to learn

In addition to working on his receiving skills, former quarterback Joe Webb also is striving to enhance his chance at a roster spot by becoming effective on special teams.

“It’s been a whole different training camp, a whole different roller coaster,” Webb said. “But I’m embracing the grind.”

But time is an adversary. Webb has to show his potential in the short time left before the start of the regular season.

Priefer said Webb would get even more special teams work against San Francisco. He will be asked to hold up gunners on the punt return team. He also will be on the kickoff coverage team and on kickoff return, where Webb will play on the front line. Priefer described Webb’s special teams performance as a “work in progress.”

“At the end of the day, we have to get ready to play Detroit on opening day,” he said. “But we know [Webb], we know the type of man he is, his high character and high work ethic, we know he’s going to improve. We have to keep that in mind as we go down this stretch here.”

Etc.

• Frazier described rookie cornerback Xavier Rhodes’ performance in Buffalo — Rhodes’ NFL debut — as up and down. “He did some good things there, but there were some other things that, when we looked at the tape, that he’ll have to get better at as we approach the regular season,” Frazier said.

• Four players missed practice Wednesday. They were fullback Jerome Felton, who will be sidelined through the end of the preseason after an appendectomy last week; wide receiver Jarius Wright, whom Frazier said needed one more day to recover from a concussion sustained in Buffalo; rookie defensive tackle Sharrif Floyd, who had a minor procedure to relieve pain in his left knee; and offensive lineman Tyler Holmes, who sat because of an ankle injury.